1. Field of the Invention
The present invention relates to an object, a process (including a method and a manufacturing method), a machine, a manufacture, or a composition of matter. In particular, the present invention relates to a semiconductor device, a display device, a light-emitting device, a driving method thereof, a manufacturing method thereof, or the like. In particular, the present invention relates to a semiconductor device, a display device, a light-emitting device, or the like including an oxide semiconductor.
In this specification, a semiconductor device includes a device which can function by utilizing electronic characteristics of a semiconductor in its category, and for example, an electro-optic device, a semiconductor circuit, and an electric appliance are included in the category of the semiconductor device.
2. Description of the Related Art
Transistors used for most flat panel displays typified by a liquid crystal display device and a light-emitting display device are formed using silicon semiconductors such as amorphous silicon, single crystal silicon, and polycrystalline silicon provided over glass substrates. Further, transistors formed using such silicon semiconductors are used in integrated circuits (ICs) and the like.
In recent years, attention has been drawn to a technique in which, instead of a silicon semiconductor, a metal oxide exhibiting semiconductor characteristics is used for transistors. Note that in this specification, a metal oxide exhibiting semiconductor characteristics is referred to as an oxide semiconductor.
For example, a technique in which a transistor is manufactured using zinc oxide or an In—Ga—Zn-based oxide as an oxide semiconductor and the transistor is used as a switching element or the like of a pixel of a display device, is disclosed (see Patent Documents 1 and 2).